210 AN INTRODUCTION TO MODERN GENETICS 



Alga Ectocarpus) the strength of the "male" and "female" fertilization 

 producing tendencies of the gametes may vary, so that one can distin- 

 guish strong and weak male and strong and weak female gametes; the 

 strength can be measured by statistical studies of the frequency of 

 conjugation when gametes of two different sorts are brought together. 

 The most important result is that gametes which react as weak males 

 towards female gametes (i.e. conjugate with them in a low percentage) 

 may act as weak females towards a strong male gamete. Hartmann 

 speaks of this as relative sexuality, and interprets it by expressing the 

 strengths of the male and female tendencies in arbitrary units. Thus, 

 denoting maleness by negative numbers and femaleness by positive 

 ones, we might have the gamete-sorts a = — 20, b = — 10, c = + 10, 

 J = -f 20, when the male and female combinations would react 

 with the strengths or frequencies ad = 40, ac = bd = 30 be = 20, 

 while the two males or the two females would react with the 

 strength 10. 



In Ectocarpus, where these facts were first discovered, the gamete 

 sexuality is not determined by genetic factors, but is dependent on the 

 sexual constitution of the plant producing the gametes, which is itself 

 determined phenotypically by unknown environmental factors. Thus a 

 plant acquires a sexuality of a certain strength which then characterizes 

 all its gametes. Hartmann has also applied a similar scheme of inter- 

 pretation to other cases, such as the multipolar sexuality of fungi 

 (p. 214), where the gamete sexuality may be directly determined by 

 genetic factors in the haplophase. 



Some authors^ have questioned whether it is yet shown that the 

 relative sexuality of the gametes in such cases as Ectocarpus is not 

 really the result of different degrees of "ripeness," which hypothesis, if 

 correct, would largely destroy the importance of the facts for a general 

 theory of sex. But this criticism can hardly apply to some of the other 

 cases recently described by Hartmann and his pupils. Thus Moewus^ 

 has investigated two species of Chlamydomonas, C. paupera, which has 

 three races, strong, middle, and weak, and C. eugametos, also with 

 different races. In the hybrid between these two species, non-disjunc- 

 tion of a sex chromosome took place, as could be shown both by the 

 inheritance of a factor lying in the chromosomes and also cytologically. 

 Of the haplophase individuals derived from the Fi, those from which a 

 chromosome was lacking because of the non-disjunction were inviable, 

 but the others, with both the sex chromosomes, survived and had a 



1 E.g. Mainx 1933. ^ Moewus 1935^ 1936. 



